Microsoft – Synching to an External Time Source

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Microsoft – Synching to an External Time Source

by Jin Kim

Most organizations setup their workstations to synchronize their time with their domain controller.  The problem arises when the server isn’t keeping the time accurately thus affecting the workstation times.  Below are instructions to ensure the responsible server is always synchronized with a reliable source.

To ensure that the clocks on your machines are more accurate in terms of absolute (and not just relative) time, you can sync the PDC Emulator in your forest root domain to one of the reliable time servers available on the Internet. This is a good idea if your company is a large enterprise with sites spanning several countries, or if your organization has two or more forests linked by forest trusts. The procedure for doing this on a PDC Emulator running Windows Server 2003 in the forest root domain is as follows. Open Registry Editor (regedit.exe) and configure the following registry entries:

  • HKLMSYSTEMCurrentControlSetServicesW32TimeParametersType

This registry entry determines which peers W32Time will accept synchronization from. Change this REG_SZ value from NT5DS to NTP so the PDC Emulator synchronizes from the list of reliable time servers specified in the NtpServer registry entry described below.

  • HKLMSYSTEMCurrentControlSetServicesW32TimeConfigAnnounceFlags

This registry entry controls whether the local computer is marked as a reliable time server (which is only possible if the previous registry entry is set to NTP as described above). Change this REG_DWORD value from 10 to 5 here.

  • HKLMSYSTEMCurrentControlSetServicesW32TimeParametersNtpServer

This registry entry specifies a space-delimited list of stratum 1 time servers from which the local computer can obtain reliable time stamps. The list may consist of one or more DNS names or IP addresses (if DNS names are used then you must append ,0x1 to the end of each DNS name). For example, to synchronize the PDC Emulator in your forest root domain with tock.usno.navy.mil, an open-access SNTP time server run by the United States Naval Observatory, change the value of the NtpServer registry entry from time.windows.com,0x1 to tock.usno.navy.mil,0x1 here. Alternatively, you can specify the IP address of this time server, which is 192.5.41.209 instead.

Now stop and restart the Windows Time service using the following commands:

net stop w32time

net start w32time

It may take an hour or so for the PDC Emulator to fully synchronize with the external time server because of the nature of the polling method W32Time uses. Depending on the latency of your Internet connection, the accuracy of the CMOS clock on your forest root PDC Emulator may be within a second or two of UTC. If you need more accurate time however, you can purchase a hardware time source like an atomic clock and connect it to your PDC emulator.

Alternatively, if you don’t want to wait for time convergence to occur between your stratum 2 time server (your forest root PDC Emulator) and the external stratum 1 time server, you can run the following command on your PDC Emulator:

w32tm /resync /rediscover

More About the Author

Jin Kim

Systems Engineer
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